We are studying some abundant, long-lived, homodisperse, low molecular weight nuclear RNA species of unknown function, particularly RNA species and D, in cultured human cervix carcinoma cells. C and D RNA exhibit several interesting characteristics: their transcription units may be up to 25 times larger than their known precursors; they seem to pass through the cytoplasm for a few minutes shortly after their transcription; and they appear to be present in heterogeneous nuclear RNA-protein particles. In addition, apparently about 5% of the cellular C and D RNA content is covalently linked to a low molecular weight subpopulation of chromatin DNA. Finally, RNA species C and D have 5'-end cap structures that are very similar to cap 2 of eukaryotic messenger RNAs, and D RNA markedly inhibits translation of mammalian messenger RNA in a cell-free extract. Several types of experiments will be performed, toward the long-term objective of identifying the physiological role of these RNA species. First, through some in vivo experiments we wish to examine if D RNA might be involved in the inhibition of protein synthesis that occurs during mitosis. Another goal is to test if RNA species D and C are translated. A third aim is to study the dynamic relationship between the covalently-linked short DNA-small RNA complexes and a) the metaphase and interphase stages of chromatin, b) the known nucleoplasmic small RNAs, and c) bulk chromatin DNA. Finally, we wish to examine by microscopic autoradiography the intracellular behavior of purified labeled low molecular weight RNA species, after they have been microinjected into cultured human cells.